Field of the Invention
The present invention relates to an exhaust case for exhausting combustion exhaust gas passing through a heat exchanger in a combustion apparatus such as an instantaneous water heating apparatus and to a combustion apparatus provided with the exhaust case.
Description of the Related Art
One example of an exhaust case is disclosed in the following Patent Literature 1 and the diagrammatical structure is shown in FIG. 4.
An exhaust case 9 shown in FIG. 4 is provided for guiding combustion exhaust gas passing upward through a heat exchanger 8, to an exhaust vent 90 and for exhausting the combustion exhaust gas outside. The exhaust case 9 includes the first and the second exhaust gas flow paths Ra, Rb. The first exhaust gas flow path Ra is formed by utilizing a water-shielding plate 91, guides combustion exhaust gas passing through the heat exchanger 8, behind the water-shielding plate 91 as shown with an arrow N11 and guides the combustion exhaust gas onto the water-shielding plate 91 toward the exhaust vent 90. The second exhaust gas flow path Rb is formed in such a manner that a lower plate 92 is provided under the water-shielding plate 91 in the forward area and a ventilation hole 93 is provided for the lower plate 92. Specifically, the lower plate 92 has a substantially horizontal plate part 92a and an upright plate part 92b extending from the rear end of the horizontal plate part 92a. A space 5e communicating with the exhaust vent 90 is formed between the horizontal plate part 92a and the water-shielding plate 91. The second exhaust gas flow path Rb guides a part of combustion exhaust gas passing through the heat exchanger 8, to the space 5e from the ventilation hole 93 and further to the exhaust vent 90.
In the above-mentioned structure, the combustion exhaust gas flowing in the exhaust case 9 diverges into the first exhaust gas flow path Ra and the second exhaust gas flow path Rb, thereby reducing exhaust noise. In addition, the above-mentioned structure suppresses combustion oscillation of the burner supplying combustion exhaust gas to the heat exchanger 8. Rain water entering the exhaust case 9 from the exhaust vent 90 is blocked by the water-shielding plate 91.
However, there is still a room for improvement in the related art as mentioned below.
Firstly, the ventilation hole 93 is provided for the horizontal plate part 92a of the lower plate 92 in the vertical direction. Therefore, combustion exhaust gas passes upward through the ventilation hole 93 and flows into the space 5e. The vertical width of the space 5e is small, so that the combustion exhaust gas hits the water-shielding plate 91 as soon as it passes through the ventilation hole 93 and a great deal of combustion exhaust gas bounces downward. Thus, the amount of combustion exhaust gas flowing into the space 5e from the ventilation hole 93 is easily reduced. In such a case, the advantageous effect of providing the second exhaust gas flow path Rb in addition to the first exhaust gas flow path Ra is reduced and a superior noise reduction effect and a suppression effect of combustion oscillation are hardly obtained. If the vertical width of the space 5e becomes remarkably large, the above-mentioned disadvantages can be partly resolved. Such a case is not appropriate because the exhaust case 9 becomes large.
Secondly, a front area 80 of the heat exchanger 8 is required to be positioned ahead of (left side in the figure) the ventilation hole 93 so as not to block the ventilation hole 93. Therefore, such a structure causes troubles in downsizing the heat exchanger 8 by reducing the width.
Thirdly, if rainwater enters the space 5e from the exhaust vent 90 for some reasons, the rain water easily flows into the ventilation hole 93. The rainwater flowing in the ventilation hole 93 enters where the heat exchanger 8 is placed, thereby causing corrosion of the heat exchanger. Prevention of such disadvantages is desired.